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Ascaphidae (tailed frogs; class Amphibia, order Anura) A monotypic family (Ascaphus truei) of amphibians, found in mountain streams in western N. America, that, like Leiopelmatidae, have nine amphicoelous vertebrae and free ribs. A muscular extension of the cloaca (‘tail’) is used in copulation. Tadpoles cling to rocks with a sucking mouth.